U.S. Pat. No. 2,554,268 discloses that emulsion copolymerizates of a butadiene-1,3 and acrylonitrile or methacrylonitrile containing less than 25% of combined nitrile are more uniform in composition and therefore possess improved general characteristics if close control of the concentration of nitrile in the reaction system is maintained. According to that patent, emulsion copolymerizates of a butadiene-1,3 and acrylonitrile or methacrylonitrile containing less than 25% of combined nitrile possess improved oil resistance, tensile strength, elongation, modulus and compression set properties provided that the nitrile is added portionwise to the reaction mixture. The improvement in the physical properties of the polymer obtained by the portionwise rather than single addition of the nitrile is greater in copolymers of lower combined nitrile content, i.e., the improvement is greater in copolymers containing 12-15% of combined nitrile than in those containing 20% of combined nitrile and greater in copolymers containing 20% of combined nitrile than in those containing 25% of combined nitrile. U.S. Pat. No. 2,378,694 discloses a method of copolymerizing a butadiene-1,3 hydrocarbon and an alpha-methylene nitrile of the formula ##STR1## where R is a member of the class consisting of hydrogen and alkyl, in the form of an aqueous emulsion in the presence of peroxynitric acid having the formula HNO.sub.4.
British Patent Specification 1,215,796 discloses an adhesive composition which comprises butadieneacrylonitrile copolymer (NBR) obtained by emulsion polymerization in the presence of dimethyl xanthogen disulfide as a molecular weight regulator. Preferably, a butadiene-acrylonitrile polymer having 25-50% by weight acrylonitrile bonded therein is used. Preferably, also the Mooney viscosity ML (100.degree. C.) of the butadiene-acrylonitrile copolymer ranges from 70 to 100. The adhesive composition of this patent specification usually comprises NBR obtained by using dimethyl xanthogen disulfide as molecular weight regulator and other ingredients such as, for example, phenol resin, filler, vulcanizing agent, vulcanization accelerator and the like, and they are usually dissolved in a solvent such as a ketone. The adhesive composition of this patent specification can be widely used as general and industrial adhesives in, for example, the shoe industry, adhesion of structural material for aircraft, brake-shoes and brake-liners of motor cars and the like.
The aforementioned adhesives either do not exhibit high levels of adhesion to high energy polymeric surfaces or exhibit a high level of finger tack.